Signal strength guided intra-cell upstream data forwarding

ABSTRACT

Intra-cell upstream data forwarding is utilized in a wireless network such as a wireless local area network. A network forwarding path is determined based on the signal strength of an access point signal received at client stations within the network, referred to as the OASS. In particular embodiments, a station that is either originating or forwarding a frame inserts its own OASS into the frame before transmitting it and a client station that receives a frame forwards it only if its own OASS exceeds the frame-enclosed OASS, illustratively by at least a predetermined amount.

CROSS-REFERENCE TO RELATED APPLICATION

This is a continuation of Ser. No. 12/653,173 filed Dec. 8, 2009 nowU.S. Pat. No. 7,983,619, which was a continuation of Ser. No.11/328,331, filed Jan. 9, 2006, now U.S. Pat. No. 7,653,355 issued Jan.26, 2010.

BACKGROUND

The present invention relates to communications in, for example,wireless local area networks, mobile/cellular and other wirelessnetworks.

In multi-hop wireless networks, such as mobile ad hoc networks, nodesstore and forward data frames for each other so the frames can beforwarded to distant destinations that are not within direct wirelesscommunication reach of data sources. Such a forwarding mechanism has notbeen adopted into wireless local area networks (WLANs). In WLANs, accesspoints are attached to a distribution system (DS), typically a wiredlocal area network (LAN), and stations and access points are withindirect communication range of each other. In other words, WLANarchitecture extends the boundaries of a distribution system by only onewireless hop. Both station to outside-of-cell (via DS) andoutside-of-cell to station types of traffic are directly between theaccess point and the station. Station to station traffic is transmittedfrom source station directly to access point then access point directlyto destination station. Thus, one might think that there is no need forclient stations to forward frames for intra-cell data forwarding,meaning the forwarding of frames to an access point by other clientstations of the same cell, i.e., communicating with the same accesspoint.

However, a closer examination of real world WLAN deployments leads to adifferent conclusion. In these systems, access points are typically atan advantage in terms of radio transmission and reception, as comparedto the client stations they serve. Access points are supplied withcommercial electrical power while client stations usually arebattery-operated. Access points may have additional signal amplificationmodules and large antenna structures, while client stations usually onlyhave the dimension-limited internal hardware of their wireless networkinterface cards. The asymmetry between the capabilities of access pointsand client stations is even more pronounced in special systems such assensor networks or other networks where the client stations (e.g.,sensor nodes) have very limited communication resources.

Because the design of WLAN protocols presumes that client stations andtheir access points are within range of each other, the coverage area ofeach cell, i.e., area served by a particular access point, is limited byclient station communication capabilities. For example, a distantstation, even if within an access point's transmission range, may not beserved by the access point because the station's own transmissions arenot strong enough to reach the access point. The superior communicationcapabilities of the access points thus can not be fully taken advantageof.

Intra-cell upstream data forwarding can help. With intra-cell upstreamdata forwarding, client stations forward other client stations'communications to the access point. This approach has the advantage ofincreasing the effective service area of each access point because nowcoverage is limited by the transmission range of the access point and nolonger that of the client stations. This effectively reduces the numberof access points required for covering an area and thus reducesdeployment costs.

In addition, intra-cell upstream forwarding also helps client stationsto conserve their valuable battery power. Each shorter transmissionconsumes less transmission power at each station, and the total energyconsumption of multiple transmissions across a certain distance is stilltypically less than what is consumed by a single long-range transmissionover the same distance.

Despite its many advantages, the intra-cell upstream forwardingmechanism has not been widely used. A significant reason relates to thecomplexity of setting up and maintaining the forwarding paths. Clientstations need to exchange control messages to learn about each others'positions relative to the access point and to compute how other stationscan be used as forwarding nodes. In mobile scenarios where clientstation positions change, thereby causing forwarding topology change,more frequent control message exchanges are required to ensure thecorrectness of forwarding path computation. These known approaches areexpensive in terms of communication, computation, and storage overhead,as well as in design and implementation complexity.

SUMMARY OF THE INVENTION

The present invention overcomes disadvantages of known intra-cellforwarding techniques. In accordance with the present invention, astation determines whether or not to forward a message (such as a packetor, more specifically, a WiFi “frame”) based on the strength of theaccess point signal received at that station. That signal strength isreferred to herein as the OASS (Observed Access point Signal Strength).

In the illustrative embodiment, in particular, a receiving clientstation forwards a message from a transmitting client station only ifthe receiving client station's OASS meets a predetermined criterion.That criterion is illustratively that a particular relationship existsbetween a) the receiving client station's OASS and b) the OASS for thetransmitting station. The relationship may be, for example, that a)exceeds b). In the disclosed embodiment, the criterion is that a)exceeds b) by at least an amount δ. That approach tends to limit theforwarders for a given frame to stations that are closer to the accesspoint than others, thereby minimizing the number of duplicate copies ofthe frame that are propagated. The value of δ may be either a pre-setconfiguration parameter for the stations or enclosed in each frame justlike the OASS.

Particular implementations of the invention implement this technique byhaving a station that is either originating or forwarding a frame insertan indication that is a function of its own OASS—illustratively anexplicit indication of the OASS—into the message before transmitting it.This enables each station that receives the message to determine therelationship between its own OASS and that of the transmitting station.

The invention offers a number of advantages. For example, it avoidsdrawbacks of known intra-cell forwarding approaches as described above.Moreover, since the WiFi protocol requires client stations to listen toaccess point traffic in a network, the design of current client stationsis readily and inexpensively modified to measure and record the accesspoint signal strength. Because there is typically ongoing traffic withinthe downlink coverage area (e.g., WiFi protocol messages, data messagesfrom access point to client stations, acknowledgements of clients' datamessages, etc.) stations within the downlink coverage area can readilycollect fresh access point signal strength data at no additional cost.In addition, the method can be carried out without the exchange ofcontrol messages and is stateless in that it can be implemented withoutany topological information being stored for data forwarding pathcomputation. The communication overhead of enclosing a small numberrepresenting the OASS in each message, or frame, is very low.

The invention is disclosed herein in the context of a wireless localarea network. However, the invention is applicable to other types ofwireless networks, such as mobile/cellular networks.

BRIEF DESCRIPTION OF THE DRAWING

In the drawing,

FIG. 1 shows a typical wireless local area network (WLAN) in which theinvention is illustratively implemented;

FIG. 2 shows a particular cell of the WLAN of FIG. 1;

FIG. 3 shows a typical frame containing a field into which a stationtransmitting the frame can insert its observed access point signalstrength (OASS), pursuant to a feature of certain embodiments of theinvention;

FIG. 4 is a flowchart of operations performed within access points andclient stations in implementing the principles of the present invention;and

FIG. 5 is a block diagram of a typical access point or client stationwithin the WLAN of FIG. 1.

DETAILED DESCRIPTION OF THE ILLUSTRATIVE EMBODIMENT

A typical wireless local area network (WLAN) in which the invention isillustratively implemented is shown in FIG. 1. In particular, EthernetLAN 10 is a distribution system that includes Ethernet switches 11 and12. Switch 11 provides a gateway for Ethernet LAN 10 to the internet 30via a router 20. Connected to switches 11 and 12 are one or morefixed-location wireless stations, referred to as access points.Specifically access points 14 and 15 are connected to Ethernet switch 11and access point 16 is connected to Ethernet switch 12. Ethernet cables13 serve as the interconnection medium for the various components justmentioned.

Access points 14, 15 and 16 have respective coverage areas 140, 150 and160. Various wireless client stations are located within the coveragearea of the several access points. The client stations are, for example,wireless-capable laptop computers, personal digital assistants or otherwireless communication devices that are moved into, out of and withinthe coverage area. At a point in time depicted in FIG. 1, clientstations 141 through 145 are located within coverage area 140, clientstations 151 through 153 are located within coverage area 150 and clientstations 161 through 163 are located within coverage area 160.

Signaling among the access point and client stations is illustrativelycarried out using a wireless network protocol based on IEEE standard802.11b, commonly referred to as WiFi. This is a packet-based protocolin which the packets are referred to as “frames.” The coverage areaboundary for a particular access point defines a region within which thestrength of signals transmitted by the access point is sufficient forclient stations to recover the content of the transmitted frames with anacceptable level of accuracy, e.g., with a particular frame error rate.As a matter of terminology for purposes of the discussion herein,references to a station being able to “receive” a frame or a signal meanthat the station is able to recover the signal/frame's informationcontent to the desired level of accuracy.

The boundaries of the coverage areas may vary somewhat over time due toa variety of factors including the movement of various objects throughthe coverage area that can change reflection patterns, as well as thepresence within the coverage area of radio signals of all kinds,including WiFi signals from other neighboring cells.

FIG. 2 shows access point 14 and client stations 141 through 145 withincoverage area 140. This FIG. is helpful in understanding intra-cellforwarding generally as well as in understanding the principles of thepresent invention. In particular, although client stations withincoverage area 140 are able to receive frames transmitted to them“downstream” by access point 14—such as over wireless link 146 betweenaccess point 14 and client station 141—this is not necessarily the casefor frames transmitted by client stations “upstream” intended for theaccess point. This is principally a result of the client stations'typically lower transmit signal strength. Thus although frames fromclient stations that are relatively close to access point 14—such asclient station 145—are received by the access point, this may not be sofor frames transmitted by the more remote client stations.

A solution to this problem is intra-cell upstream data forwarding.Upstream communications from remote client stations within the cellproceed over multiple short range links from one station to another,with the frame ultimately arriving at the access point. (In addition,station-to-station frames are delivered to the access point via upstreamdata forwarding, then directly from the access point to the destinationstation.) As noted above, the known intra-cell data forwardingtechniques of flooding the cell and topology based forwarding techniquesuch as mobile ad hoc network (MANET) routing consume an undesirablylarge amount of resources.

The present invention is directed to a technique, referred to asSignal-Strength-Guided-Intra-Cell Forwarding (SGIF), that overcomesdisadvantages of prior approaches such as flooding and topology basedforwarding. In accordance with the present invention, a stationdetermines whether or not to forward a message, e.g., packet, based onthe strength of the access point signal received at that station, thatsignal strength being referred to herein as the OASS (Observed Accesspoint Signal Strength).

In the illustrative embodiment, in particular, a receiving clientstation does not retransmit a frame addressed to another station if theOASS for the receiving station is, or at least appears to be, lower thanthe OASS of the transmitting client station, i.e., the client stationfrom which the frame was received. Particular implementations of theinvention implement this technique by having a station that is eitheroriginating or retransmitting (“forwarding”) a frame insert its own OASSinto the frame before transmitting it. This enables each receivingstation to compare its own OASS to the OASS of the transmitting stationand to make the above determination.

The invention takes advantage of the fact that due to propagation pathloss, the OASS generally decreases as the receivers get farther awayfrom the access point. (The opposite, although not entirely impossible,is rare.) Thus, if the signal strength serves as an “elevation mark” thepeak will be located exactly where the access point is. The direction of“elevation” increase also coincides with the direction of upstream dataforwarding.

There are several places for the OASS to be enclosed within a standardWiFi frame. FIG. 3 shows an illustrative WiFi frame format 300 in whichan OASS field 32 is inserted between MAC header 31 and frame body 33. Instandard WiFi frames the IEEE 802.11 MAC header 31 is immediatelyfollowed by frame body 33, which is the payload (data) portion of theframe, and then the checksum Frame Check Sequence (FCS) field 34. Inthis illustrative example, it is assumed that the present invention isimplemented in an SGIF module above the common WiFi MAC layer, asdescribed in further detail below in connection with FIG. 5. Thus areasonable place to insert the OASS field 32 is after the MAC header 31as shown in FIG. 3. Doing so, the OASS field 32 and the data fieldtogether appear as the frame body 33 to the standard WiFi MAC layer.Once the WiFi MAC layer finishes processing, both the OASS field 32 anddata will be passed up to the SGIF module implementing the presentinvention for processing. This module will process and strip away theOASS field 32 and only passes the true data portion of the frame tohigher layers. If one were able to modify the standard IEEE 802.11 frameformat and blend the implementation of the present invention within thestandard WiFi MAC layer, the OASS field 32 can be alternatively placedwithin the WiFi MAC header 31. The OASS within field 32 is referred toherein as the “frame-enclosed OASS.”

In particular embodiments, the above-stated criterion—i.e., that areceiving client station does not retransmit a frame if its OASS is, orat least appears to be, lower than the OASS of the transmitting clientstation—is implemented by the receiving station forwarding a frame basedon a determination that the OASS for the receiving station exceeds theOASS for the transmitting station. In the present disclosed embodiment,however, a further constraint is applied. In particular, a stationretransmits a frame only if its own OASS exceeds the frame-enclosed OASSby at least an amount δ. In other words, only if a station's OASS isgreater than the quantity [frame-enclosed-OASS+δ] does it retransmit theframe. This, in effect, limits the forwarders of a frame to stationsthat are within a zone whose size is determined by the parameter δ. Thisconserves network resources by controlling the number of instances of aparticular frame being forwarded throughout the network. The value of δmay be either a pre-set configuration parameter for the stations that,for example, the access point distributes or it may be enclosed in eachframe just like the OASS. In the latter case, the value of δ could bedetermined by the transmitting station based on traffic observations orother historical data, thereby tailoring the value δ to one thatachieves a desirable balance between a) frame delivery assurance and b)limiting the number of stations involved in forwarding the frame.

The foregoing is illustrated in FIG. 2 relative to communicationsbetween access point 14 and client station 141. As shown in FIG. 2,client station 141 is able to receive communications from access point14 over single-hop access-point-to-station wireless link 146. However,the signal strength of client station 141 is too weak for access point14 to receive communications from client station 141 directly. Framestransmitted by client station 141 can, however, be received by clientstations that are closer to client station 141 than access point 14. Inthis example, it is assumed that client station 141 has just transmitteda frame and that client stations 142, 143 and 144 all receive thatframe. As indicated in FIG. 2, the strength of the signal from accesspoint 14 most recently observed at client station 141—its OASS—is −85dBm. That OASS value was inserted into OASS field 32 (FIG. 3) by clientstation 141 before the frame was transmitted. As indicated in FIG. 2,the OASS for client station 142 is −87 dBm, which is less than the −85dBm value in OASS field 32. (Since the signal strengths are negativenumbers, the value of a particular OASS exceeds that of another OASS ifits absolute value is smaller. Thus, −85 dBm>−87 dBm.) Accordingly,client station 142 does not retransmit the frame.

The OASS for client station 143 is −75 dBm, which is greater than theOASS of −85 dBm contained in field 32. In some embodiments of theinvention, this may be sufficient for client station 143 to retransmitthe frame. In the present illustrative embodiment, however, it is notenough for a potential forwarder's own OASS to simply exceed theframe-enclosed OASS in order for the potential forwarder to actuallyretransmit the frame. Rather, in this embodiment the potentialforwarder's OASS must exceed the frame-enclosed OASS by at least anamount δ. In this example, δ=15 dBm. That is, a potential forwardingstation's OASS must exceed the OASS contained within field 32 by atleast 15 dBm in order for the receiving station to retransmit the frame.Although the OASS for client station 143 exceeds that of client station141, the difference is only 10 dBm, which is less than the requireddifference of 15 dBm. Accordingly, client station 143 does notretransmit the frame either.

By contrast, the OASS for client station 144 is −65 dBm, which exceedsthe −85 dBm contained in field 32 by 20 dBm. Accordingly, client station144 does retransmit the frame.

Before retransmitting the frame, however, client station 144 overwritesthe OASS field 32 with its own OASS of −65 dBm. That retransmitted frameis illustratively received by all of the client stations shown in FIG. 2but not by access point 14. Client station 141 does not retransmit theframe since it was the originator of the frame. Client stations 142 and143 do not retransmit the frame since their OASS's are less than the −65dBm that client station 144 inserted in field 32 prior to retransmittingthe frame.

However, the OASS for client station 145 is −35 dBm, which exceeds the−65 dBm contained in field 32 by 30 dBm. Accordingly, client station 145does retransmit the frame. Moreover, the signal strength of clientstation 145 is sufficient for the frame to be received by access point14. It is thus seen that the original frame transmitted by clientstation 141 has made its way to access point 14 over a signal pathcomprising multiple short-range links 147, 148 and 149.

In this simple example, the frame reaches access point 14 over only onesignal path. In general, however, multiple paths each meeting thecriteria for cell forwarding at each hop may occur, resulting inmultiple copies of the frame reaching access point 14. The WiFi protocoland higher layer protocols such as IP enable the access point or thefinal destination of the communication to recognize duplicate frames andto discard all but one.

The processing carried out by an access point or a client station uponthe receipt of a frame is illustrated in FIG. 4. This processing isillustratively carried out at the data link layer of the WiFi protocol.

After the frame is received at 410, the process differs for accesspoints and for client stations. Access points and stations are typicallyconfigured at the time of manufacture or deployment in such a way thatthey can determine what kind of node they are. If the receiving nodedetermines, at 412, that it is an access point, it needs to send back anacknowledgement (ACK) of the frame at 420, pursuant to the WiFiprotocol. It is then determined at 422 whether the frame is destined fora station within the same cell. The access point is aware of the MACaddresses of all of the client stations within its cell and can thusmake that determination. If the frame is destined for a station withinthe same cell, then the access point transmits the frame to that stationat 426. If the frame is not addressed to a station within its cell, thenat 424 the access point forwards the frame to the distribution system(DS), that is, to Ethernet LAN 10 and, more specifically, to the accesspoint's attached Ethernet switch. From there the frame is transmittedwithin Ethernet LAN 10 or outside of the LAN via the internet, dependingon the location of the destination station.

Returning to decision point 412, and assuming that the receiving node isa client station rather than an access point, the client station needsto determine, at 430, whether the frame is from its serving access pointas can be determined from the BSSID field and the source MAC addresswithin the frame's MAC header. If the frame is from the access point,the OASS value stored locally within the client station (e.g., instorage location or register 575 described below in conjunction withFIG. 5) is updated at 460 using the OASS that was most recently measuredat the OSI physical layer (as also described below). That OASS willtypically be the OASS associated with the frame currently beingprocessed. If, as determined at 462, the frame is not destined for thereceiving station itself, the received frame is dropped at 466.Otherwise, at 464, the frame is passed to the upper layers of the WiFiprotocol stack for further processing.

Returning to decision point 430, and assuming that the received frame isnot from the access point, the receiving station needs to check at 440if the frame is for itself. If it is, the received frame is passed at442 to the upper layers of the WiFi protocol stack for furtherprocessing. If the frame is not intended for the receiving station, thereceiving station is a potential forwarder of the frame. Accordingly,the station determines at 450 whether its own OASS exceeds theframe-enclosed OASS by more than δ, denoted in FIG. 4 as MY OASS>δ+FRAMEOASS. If it is not, the receiving station drops the frame at 456.Otherwise, the receiving station is to forward, i.e., retransmit, theframe at 454. Before doing so, however, the station overwrites OASSfield 32 with its own OASS at 452.

As a result of the sequence of operations just described, a frame isforwarded towards the access point and eventually reaches the accesspoint.

A client station transmitting a frame needs to ascertain that the framewas received. The WiFi protocol supports an acknowledgement schemewherein a station that receives a frame sends an acknowledgement messageto the frame transmitter after successfully receiving a data frame. If atransmitting station does not receive an acknowledgement within a presettimeout period, it assumes that the message was not received and itinitiates a re-transmission. Such an explicit acknowledgement scheme, ifintra-cell forwarding is implemented, results a chain of hop-by-hopdata-acknowledgement exchanges. Although such a scheme improvestransmission reliability, disadvantageously, however, having eachreceiving client station acknowledge each frame that it receives andforwards will consume significant amounts of air time and battery power.

In the present embodiment, however, such acknowledgements are not sentby each forwarding station. Rather, the illustrative embodiment usesimplicit acknowledgements. By this is meant that after a stationtransmits a frame, it knows the frame was received by some next hopclient station—and that forwarding is in progress—if it overhears aretransmission of the frame by some client station, and thus it knowsthat it need not re-send the frame even in the absence of an explicitacknowledgement. This is known as the implicit acknowledgement becausethe retransmission of the same data frame implies the successfullyreception of the frame by the forwarder. If a station does not overheara retransmission of the frame within a particular preset period of time,then it re-sends it.

The access point does, nonetheless, need to eventually explicitlyacknowledge the reception of the frame. In this case since the dataframe is not forwarded further, implicit acknowledgement is no longer anoption. Both implicit acknowledgement as described in the previousparagraph and explicit acknowledgement from the access point informs aforwarding station that the forwarded frame has been receivedsuccessfully. If neither is detected within a particular preset periodof time a station involved in the frame forward initiates retransmission(re-forwarding) of the data frame. This function can be implemented by atimer similar to the standard WiFi acknowledgement timer.

This access point acknowledgement actually serves three purposes: a) toexplicitly acknowledge the last forwarder, b) to inform all clientstations in the cell there is no need to forward this frame any more,and c) to acknowledge to the original source of the frame that thedelivery was successful. Although the original source learns that itsdata frame is being forwarded from the implicit acknowledgements fromthe first hop forwarders, if the forwarding fails farther down theforwarding path and the forwarder gives up trying after a preset numberof attempts, the original source may not be aware of such failurebecause the lack of implicit acknowledgement is beyond the receptionrange of the original source. The final explicit acknowledgement fromthe access point ultimately answers the question of whether the dataframe has arrived at the access point. An acknowledgement timer similarto the standard WiFi acknowledgement timer—except that the presetexpiration time of this timer takes multi-hop intra-cell forwardingoperations into consideration and thus is typically longer—is needed forthe original source. If no acknowledgement from the access point isreceived before this timer expires, the source station's SGIF modulewill try to resend the data frame for a preset number of times before itdeclares “unable to transmit to access point” to its upper layers.

In general, each time a frame is retransmitted, it gets closer to theaccess point. However, while a frame is being forwarded, if after aparticular forwarder there are no other stations having higher OASSwithin the reach of this forwarder, the frame forwarding path is broken.A station can discover that it is the last hop before a gap along theforwarding path by observing the lack of implicit acknowledgement fromother forwarder or explicit acknowledgement from the access point forits transmissions. The analogy of this situation in mountain climbing isthat a climber has reached the top of a small peak before the real peak.So to get to the real peak, he/she would have to step down from thesmall peak first. In the SGIF case, the equivalent of “stepping down” isfor the forwarder—having determined that its frame was not retransmittedby another station—to retransmit the frame with an artificially reducedOASS. (In embodiments in which, as suggested above, δ is also embeddedin each frame, the same effect can be achieved by making the value of δsmaller or even negative.) This way the forwarding path may temporarilyback track to stations farther away from the access point and hopefullyother successful forwarding paths along different directions can beexplored from there.

FIG. 5 is a block diagram of a station implementing the SGIF techniqueof the present invention. The FIG. represents both client stations andstations that are access points. The station is in two parts—WiFinetwork interface card, or NIC, 50 and host computer 60. In particular,NIC 50 includes radio 52; baseband processor 53 which implements thephysical layer of the WiFi communication stack; medium accesscontroller, or MAC, 57, which implements a sub-layer of the data linklayer of the WiFi communication stack and is sometimes referred to as“lower MAC”; and host computer interface 59. These are all connected toa bus 54 and are controlled by embedded central processing unit, or CPU,55 having an associated memory 56, both of which are also connected tobus 54.

The above are standard network interface card components known in theart and in current commercial use and need not be described in furtherdetail except with respect to their involvement in implementing thepresent invention. In particular, the software in MAC 57 includes“standard” WiFi MAC 571 implementing standard MAC functions. Oncestandard WiFi MAC 571 layer finishes its processing of a received frame,that frame is passed up to SGIF module 572 that implements certain ofthe illustrative functions implementing the invention as set forth inFIG. 4—illustratively, functions 410, 412, 430 and 460. Specifically,SGIF module 572 obtains the current OASS for the station (denoted MYOASS) using a conventional MAC command that queries baseband processor53 for this piece of information. The value of MY OASS thus received isstored in memory location 575 associated with SGIF module 572.

In other embodiments, any or all of the MAC functionality, including thefunctionality of the SGIF module, can be implemented using any desiredtechnology, including any combination of hardware, software, digitalsignal processors, and the like. In some such implementations, the OASSobtained by SGIF module 572 as just described might be stored in adesignated hardware register rather than in a general purpose memorylocation, in which case reference numeral 575 would be understood asreferring to such a register.

Host computer 60 includes CPU 63, storage 62 and memory 64. The lattercontains link layer software 65 and software 66 implementing the upper(network, transport, session, presentation and application) layers ofthe protocol stack. Link layer software 65 includes the portion of theMAC sublayer not included in “lower MAC” 57 in network interface card50. That portion is “upper MAC” 67. Link layer software 65 furtherincludes software 68 implementing the non-MAC portion of the link layer.

Upper MAC 67 includes “standard” MAC 671 implementing those aspects ofthe standard MAC sublayer not implemented by lower MAC 57. MAC 67 alsoincludes SGIF module 672 implementing the remainder of the functionsshown in FIG. 4, i.e., all of the functions except for functions 410,412, 430 and 460, that implement the principles of the presentinvention. The value of MY OASS passed to SGIF module 672 is stored inmemory in a location denoted 675.

Although not explicitly discussed herein, those skilled in the art areaware that frames that are originated by host computer 60 are processeddown through the protocol stack from upper layers 66 through link layersoftware 65 and then into network interface card 50 for lower MAC andphysical layer processing before being transmitted by radio 52.

The foregoing merely illustrates the principles of the invention andmany alternative arrangements embodying the principles of the inventionare possible.

For example, although the δ parameter may limit the size of theforwarding zone, duplicated forwarding may still occur. Duplicatedforwarding may not necessarily be disadvantageous because it improvesdata forwarding reliability. It is nonetheless less desirable in systemswhere redundant transmission should be kept to a minimum. In such acase, an optional SGIF technique may be employed. That is, instead ofsimply comparing OASS's, potential forwarders may execute a back-offmechanism as do transmitters in many contention-based systems. After apotential forwarder receives a frame and determines, based on its OASS,that it can forward the frame, it does not immediately do so but,rather, it starts a back-off timer. The initial duration setting of thetimer should be reversely correlated (for example, inverselyproportional, either linearly or exponentially) to the differencebetween the potential forwarder's OASS and the enclosed OASS in thereceived frame. That is, the smaller the OASS difference, the longer thetimer duration setting. While this timer is counting down, the stationobserves whether any other client station forwards the same frame. Ifsome other station does forward the same frame, this potential forwardergives up by dropping the frame. The fact that some other station alreadyforwarded the frame means that that other station has a higher OASS andis thus closer to the access point. If the timer expires and no otherstation was observed to have forwarded the frame, then this stationforwards it. Using this approach, forwarders closer to the access pointare given preference and duplicated forwarding is eliminated or reduced.

The above-described back-off technique can be used to implementembodiments of the invention that do not require the enclosing of theOASS in the frames. Instead, a pre-set “lowest possible,” or “floor,”OASS value would be used in the calculation of the initial durationsetting of the countdown timer instead of the enclosed OASS. Althoughthis approach increases the waiting period before a client stationdecides to forward, it does have the advantage of not requiring anyframe format change and may be appealing for situations in which anychange of frame format is not feasible or is regarded as undesirable.

Other variations are possible. For example, as previously noted, theinvention can be implemented in networks other than wireless LANs.Moreover, stations participating in the communications and implementingthe invention may be other than entities that function as WLAN “accesspoints” and/or as “client stations.” That is, forwarding pursuant to theprinciples of the invention may be carried out in a network comprisingentities other than those which might be characterized as “accesspoints” or “client stations.”

In some applications, it might be found desirable to retain within aframe a list of the OASS's of each station in the forwarding path,rather than having each station overwrite the value at each forwardingstation. Moreover, although as previously noted the invention can beimplemented without the exchange of control messages and without anytopological information being stored for data forwarding pathcomputation, the invention might be implemented in conjunction withthese if it were to prove advantageous.

Although in the disclosed embodiment an indication of the OASS isenclosed within the frames, an indication that is a function of theOASS, such as only its most significant bits or some other parameterthat is dependent upon the OASS, might be used.

It is possible in embodiments in which the OASS is enclosed withinframes that this will be done selectively. As but one example, a clientstation may withhold inserting its OASS in a frame if, for example, itknows that it is sufficiently close to the access point that the framewill not need to be forwarded through another client station.

In applications that use the parameter δ per the description above, thevalue of that parameter might be dynamically adapted depending on, forexample, one or more network and/or cell performance measures.

Although the disclosed embodiment divides the functionality of a stationin implementing the invention between two components, a networkinterface card and a host computer, those functions may both beimplemented in one or the other of those components, or in other systemcomponents. Moreover any or all aspects of the WiFi protocol, includingthose which implement the present invention, may be realized inhardware, software, firmware, microcode or any desired technology.

Downlink communications do not need to use the same communicationtechnology as the uplinks. For example, in applications where datatraffic is largely from clients to access points, the downlink may use alow bandwidth but long range communication technology to cover a largearea. Depending on system requirements, even non-RF technologies such asoptical and acoustic may be used as downlinks as long as the OASSmeasure is still available to the client stations.

It will thus be appreciated that those skilled in the art will be ableto devise numerous arrangements that, although not explicitly shown ordescribed herein, implement the principles of the invention and arewithin their spirit and scope.

The invention claimed is:
 1. A method for use in a wireless networkcomprising a first station and a plurality of second stations, themethod being performed by a receiving one of the second stations thathas received a message from a transmitting one of the second stations,the method comprising determining whether said receiving station shouldforward said message within the wireless network, said determining beingbased on an observed signal strength of a signal received by saidreceiving station from the first station, and if the determining is thatsaid receiving station should forward said message within the wirelessnetwork, then forwarding said message within the wireless network butonly if a) said signal strength observed by said receiving station isgreater than b) a signal strength of a signal received by saidtransmitting station from the first station, and inserting in saidmessage, prior to said receiving station forwarding said message, asignal strength indication that is a function of the strength of asignal that had been received by said receiving station from said firststation, wherein an indication that is a function of said signalstrength b) is included in the received message, and wherein the methodfurther comprises re-forwarding said message upon a determination thatsaid message may not have been received by any other station, the signalstrength indication in the re-forwarded message being made lower thansaid signal strength indication in the message when previouslyforwarded.
 2. A method for use in a wireless network comprising a firststation and a plurality of second stations, the method being performedby a receiving one of the second stations that has received a messagefrom a transmitting one of the second stations, the method comprisingdetermining whether said receiving station should forward said messagewithin the wireless network, said determining being based on an observedsignal strength of a signal received by said receiving station from thefirst station, wherein said receiving station forwards said messagewithin the wireless network only if said signal strength observed bysaid receiving station is greater than a signal strength of a signalreceived by said transmitting station from the first station by at leasta predetermined amount δ, and wherein an indication of saidpredetermined amount δ is included in the received message.
 3. A methodfor use in a packet-based wireless network comprising an access pointand a plurality of client stations located within a cell associated withthe access point, the method being performed by a receiving one of theclient stations that has received a packet from a transmitting one ofthe client stations, the method comprising forwarding the receivedpacket within the cell only if a particular relationship exists betweena) a signal strength of a signal that had been received from the accesspoint by the receiving client station and b) a signal strength of asignal that had been received from the access point by the transmittingclient station, wherein said particular relationship is that said signalstrength a) is greater than said signal strength b) by at least apredetermined amount δ, and wherein an indication of said predeterminedamount δ is included in the received packet.
 4. The invention of claim 3wherein said receiving station forwards said packet unless it determinesthat another one of the client stations has forwarded the packet withinthe network prior to a particular time period having elapsed after saidreceiving station receives said packet, said particular time periodhaving a duration that is a function of said observed signal strength.